This invention relates to a diaphragm type control valve to be used in a valve such as an intake air control valve and secondary air bypassing valve, particularly, to a new structure which enables switching over the valve operation from a short period opening to a long period opening, and vice versa.
In a conventional secondary air injection device employed in an exhaust gas purifying system for an engine, an intake air control valve and a secondary air bypassing valve have used for prevention of afterburn which takes place in the course of engine deceleration. In the valve mentioned above, there is provided a diaphragm having an orifice therein through which air flows until the pressure of two chambers divided by the diaphragm has been equalized after engine deceleration so that the valve opening period is determined. By setting the valve opening period, when the engine is decelerated the intake air control valve supplies air derived from an air pump to the intake port of the engine in a few seconds, thus proportioning the air fuel ratio to prevent misfires, and, the secondary air bypassing valve cuts the air injected into the exhaust port in the same few seconds, thus preventing the explosion of incompletely combusted gases in the exhaust pipe which is referred to as afterburn.
However, the time in which the misfires occur at the engine deceleration largely depends on engine temperature, and it is longer when the engine is cold than that when the engine is warmed up.
If the valve opening period is set to suit the warmed-up engine condition, it is too short when the engine is cold, resulting in misfires after the intake air control valve has stopped supplying air, and in turn, afterburns.
On the other hand, in the secondary air bypassing valve, the air injected into the exhaust port is cut during the valve opening period and, as a matter of course, the exhaust gas purification is stopped. Cut-off time of the air injection should be as short as possible for the exhaust gas purification.